1. Field of the Invention
Aspects of the present invention relate to an electron emission display, and more particularly, to an electron emission display that can effectively focus electron beams emitted from electron emission regions by improving a focusing electrode.
2. Description of the Related Art
Generally, electron emission elements are classified into those using hot cathodes as an electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission elements, including Field Emitter Array (FEA) elements, Surface Conduction Emitter (SCE) elements, Metal-Insulator-Metal (MIM) elements, and Metal-Insulator-Semiconductor (MIS) elements.
The FEA element includes electron emission regions and cathode and gate electrodes that are driving electrodes. The electron emission regions are formed of a material having a relatively low work function or a relatively large aspect ratio, such as a molybdenum-based material, a silicon-based material, and a carbon-based material such as carbon nanotubes, graphite, and diamond-like carbon so that electrons can be effectively emitted when an electric field is applied thereto under a vacuum atmosphere. When the electron emission regions are formed of the molybdenum-base material or the silicon-based material, they are formed in a pointed tip structure.
Generally, the electron emission elements are arrayed on a first substrate to form an electron emission device. The electron emission device is combined with a second substrate, on which a light emission unit having phosphor layers and an anode electrode are formed, to establish an electron emission display.
That is, the conventional electron emission device includes electron emission regions and a plurality of driving electrodes functioning as scan and data electrodes. By the operation of the electron emission regions and the driving electrodes, the on/off operation of each pixel and an amount of electron emission are controlled. The electron emission display excites phosphor layers using the electrons emitted from the electron emission regions to display a predetermined image.
The first and second substrates are sealed together at their peripheries using a sealing member and the inner space between the first and second substrates is evacuated to form a vacuum envelope. In addition, a plurality of spacers is disposed in the vacuum envelope to prevent the substrates from being damaged or broken by a pressure difference between the inside and outside of the vacuum envelope.
The spacers are exposed to the internal space of the vacuum envelope in which electrons emitted from the electron emission regions move. Therefore, the spacers are charged with positive or negative electric charges by the electrons colliding therewith. The charged spacers may change the electron beam path by attracting or repulsing the electrons. As a result, a non-emission region of the phosphor layer increases.
For example, when the spacers are charged as the positive electric charge, the spacers attract the electrons such that a relatively large amount of electrons collides with a portion of the phosphor layer near the spacers. As a result, the luminance of the portion around the spacers is higher than those of other portions. In this case, the spacers may be detected on a screen. In order to prevent the change of the electron beam path, the spacers may be coated with an insulation material or may be connected to the electrodes.